Root-secreted peptide pep1 in rice and gene encoding the same and use thereof

ABSTRACT

The disclosure isolates and identifies a peptide PEP1 that regulates plant root development and a gene OsPEP1 encoding the same. Exogenous application of PEP1 could inhibit the plant root development. A recombinant expression vector containing the gene or part of the DNA of the gene is obtained, and a transgenic plant with altered root growth and development is obtained by transforming with the recombinant expression vector. Therefore, the peptide can be used as a plant growth regulator, and the gene encoding the same and precursor protein thereof can be used as a potential molecular breeding target for crop improvement, for example, improving crop yield by regulating the growth and development of crop roots.

CROSS REFERENCE TO RELATED APPLICATION

This patent application claims the benefit and priority of Chinese Patent Application No. 202110194477.8, entitled “Root-Secreted Peptide PEP1 in Rice and Gene Encoding the Same and Use Thereof” filed on Feb. 20, 2021, the disclosure of which is incorporated by reference herein in its entirety as part of the present application.

TECHNICAL FIELD

The disclosure relates to the field of biotechnology, in particular to the use of a plant root-secreted peptide and a gene encoding the same in regulation of the growth and development of plant roots.

BACKGROUND ART

Roots are important underground organs of plants, which not only support plants, but also take up nutrients, water and other substances from soil for plant growth and development. In addition, the root system of plants also monitor various signal molecules in the soil, such as moisture content, nutrient levels, and plant hormones, to improve plant adaptability (Meng et al. 2019). Plant roots are mainly divided into two categories, tap root system and fibrous root system. Rice is a monocotyledonous model plant with a fibrous root system consisting mainly of seminal root, adventitious root, and lateral root and root hair (Rebouillat et al. 2009; Coudert et al. 2010). Studies have shown that a high root-to-shoot ratio and a well-developed root system can improve rice drought resistance and yield (Fukai et al. 1995; Gowda et al. 2011). Previous studies have shown that the growth and development of rice roots are strictly regulated by exogenous signals and endogenous genetic programs (Benfey et al. 2012; Orman-Ligeza et al. 2013).

Previous studies have shown that peptides act as exogenous signal molecules to regulate root development in Arabidopsis (Oh et al., 2018). Exogenous application of synthetic peptide root meristem growth factor 1 (RGF1) restores the apical meristem-deficient phenotype in tpst-1 mutants, suggesting that RGF1 is required for the maintenance of apical stem cells (Matsuzaki et al. 2010). Further genetic analysis reveals that RGF/GLV controls the abundance and trafficking dynamics of the auxin efflux carrier PINFORMED 2 in root meristem through a post-transcriptional regulatory mechanism, thereby regulating the size of plant root apical meristem (Whitford et al. 2012). The size of plant root tip meristem is also regulated by the CIF. (CLAVATA 3 (CLV3)/EMBRYO SURROUNDING REGION (ESR)-related) family of peptides. There are 32 genes encoding the CLE peptides in Arabidopsis, and those peptides can be divided into two groups: A-type CLE and B-type CLE. Type A CLE peptides play roles in root meristem development, while type B CLE peptides are involved in root vascular bundle development (Cock and McCormick 2001; Whitford et al. 2008). For example, the type A CLE peptide CLE40 is required for columnar cell differentiation, and the loss-of-function mutant cle40 exhibits an irregularly shaped root tip due to the delayed differentiation of columella cells, thereby exhibiting a short root phenotype (Stahl et al. 2009). Other CLE peptides such as CLE26, CLE40 and CLE45 control primary root growth by regulating primary epithelium formation during vascular bundle development (Depuydt et al. 2013; Rodriguez-Villalon et al. 2014; Rodriguez-Villalon et al. 2015; Hazak et al. 2017). In addition, the tyrosine sulfated peptides PHYTOSULFOKINE (PSK) and PLANT PEPTIDE CONTAINING SULFATED TYROSINE 1 (PSY1) can promote primary root growth by regulating cell expansion in the elongation/meristematic zone (Amano et al. 2007; Kwezi et al. 2011; Hartmannet et al. 2014; Ladwiget et al. 2015). The peptide CASPARIAN STRIP INTEGRITY FACTOR 1 (CIF1) is essential for casparian strip formation, as CIF1 loss-of-function mutants exhibit severe growth retardation at high iron concentrations, while these defects can be fully recovered by exogenous application of CIF1 peptide (Nakayama et al. 2017).

Compared with Arabidopsis, the mechanism by which peptides regulate rice root growth and development is still unclear. Therefore, it is very important and necessary to isolate and identify peptides related to rice root growth and development, and to determine genes encoding these peptides to further fully understand the mechanism of root development of rice and other monocots, and to obtain desired genes for the breeding of new rice cultivars.

REFERENCES

-   Amano Y, Tsubouchi H, Shinohara H et al (2007) Tyrosine-sulfated     glycopeptide involved in cellular proliferation and expansion in     Arabidopsis. Proc. Natl. Acad. Sci. U.S.A. 104, 18333-18338. -   Benfey P N (2012) Toward a Systems Analysis of the Root. Cold Spring     Harbor Symposia on Quantitative Biology 77, 91. -   Cock J and McCormick S (2001) A large family of genes that share     homology with CLAVATA3. Plant Physiol. 126, 939-942. -   Coudert Y. B{tilde over (e)}s M, Le T V et al (2011) Transcript     profiling of crown rootless 1 mutant stem base reveals new elements     associated with crown root development in rice. BMC Genomics 12,     1-12. -   Coudert Y. Perin C, Courtois B et al (2010) Genetic control of root     development in rice, the model cereal. Trends Plant Sci. 15,     219-226. -   Depuydt S. Rodriguez-Villalon A, Santuari L et al (2013) Suppression     of Arabidopsis protophloem differentiation and root meristem growth     by CLE45 requires the receptor-like kinase BAM3. Proc. Natl. Acad.     Sci. U.S.A. 110, 7074-7079. -   Fukai S, Cooper M (1995) Development of drought resistant cultivars     using physio-morphological traits in rice. Field Crops Res. 40,     67-87. -   Hartmann J. Fischer C, Dietrich P et al (2014) Kinase activity and     calmodulin binding are essential for growth signaling by the     phytosulfokine receptor PSKR1. Plant J. 78, 192-202. -   Hazak O, Brandt B. Cattaneo P et al (2017) Perception of root-active     CLE peptides requires CORYNE function in the phloem vasculature.     EMBO Rep. 18, 1367-1381. -   Kwezi L, Ruzvidzo O, Wheeler J I et al (2011) The phytosulfokine     (PSK) receptor is capable of guanylate cyclase activity and enabling     cyclic GMP-dependent signaling in plants. J. Biol. Chem. 286,     22580-22588. -   Ladwig F, Dahlke R I, Stührwohldt N et al (2015) Phytosulfokine     regulates growth in Arabidopsis through a response module at the     plasma membrane that includes CYCLIC NUCLEOTIDE-GATED CHANNEL 17,     H+-ATPase, and BAK1. Plant Cell 27, 1718-1729. -   Lv Q, Zhong Y, Wang Y et al (2014) SPX4 negatively regulates     phosphate signaling and homeostasis through its interaction with     PHR2 in rice. Plant Cell 26, 1586-1597. -   Matsuzaki Y, Ogawa-Ohnishi M, Mori A et al (2010) Secreted peptide     signals required for maintenance of root stem cell niche in     Arabidopsis. Science 329, 1065-1067. -   Meng F, Xiang D, Zhu J et al (2019) Molecular mechanisms of root     development in rice. Rice 12, 1. -   Nakayama T, Shinohara H, Tanaka M et al (2017) A peptide hormone     required for Casparian strip diffusion barrier formation in     Arabidopsis roots. Science 355, 284-286. -   Orman-Ligeza B, Parizot B, Gantet P P et al (2013) Post-embryonic     root organogenesis in cereals: branching out from model plants.     Trends Plant Sci. 18, 459-467. -   Rebouillat J, Dievart A, Verdeil J L et al (2009) Molecular genetics     of rice root development. Rice 2, 15-34. -   Rodriguez-Villalon A. Gujas B, Kang Y H et al (2014) Molecular     genetic framework for protophloem formation. Proc. Natl. Acad. Sci.     U.S.A. 111, 11551-11556. -   Rodriguez-Villalon A, Gujas B, van Wijk R et al (2015) Primary root     protophloem differentiation requires balanced     phosphatidylinositol-4,5-biphosphate levels and systemically affects     root branching. Development 142, 1437-1446. -   Stahl Y, Wink R H, Ingram G C et al (2009) A signaling module     controlling the stem cell niche in Arabidopsis root meristems. Curr.     Biol. 19, 909-914. -   Wang W J, Li C Y, Li M S (2019) Construction of an expression vector     of GPC-3 CTL epitope. Journal of Southern Medical University 29,     1548-1550. -   Whitford R, Fernandez A, De Groodt R et al (2008) Plant CLE peptides     from two distinct functional classes synergistically induce division     of vascular cells. Proc. Natl. Acad. Sci. U.S.A. 105, 18625-18630. -   Whitford R. Fernandez A, Tejos R et al. (2012) GOLVEN secretory     peptides regulate auxin carrier turnover during plant gravitropic     responses. Dev. Cell 22, 678-685.

SUMMARY

The technical problem to be solved by the present disclosure is to provide a peptide for regulating plant root development and a gene encoding the same and use thereof.

In order to solve the technical problem, the present disclosure provides a use of a peptide for regulating plant root development in treatment of a plant, in which a root length of the plant is shortened or lengthened upon the treatment;

the peptide is selected from the group consisting of:

-   -   a peptide having the amino acid sequence set forth in SEQ ID NO:         1; and     -   a peptide derived from the peptide having the amino acid         sequence of set forth in SEQ ID NO: 1 with a substitution and/or         a deletion and/or an addition of one or more amino acid residues         thereof, and being related to regulation of plant root         development.

In some embodiments of the use of the peptide in regulation of plant root development in the present disclosure:

-   -   a precursor protein of the peptide is selected from the group         consisting of a precursor protein having the amino acid sequence         set forth in SEQ ID NO: 2; and     -   a precursor protein derived from the precursor protein having         the amino acid sequence set forth in SEQ ID NO: 2 with a         substitution and/or a deletion and/or an addition of one or more         amino acid residues thereof, and being related to plant         development;

The present disclosure provides a use of a gene for regulating plant root development in constructing a transgenic plant, in which a root length of the transgenic plant is shortened or lengthened upon treatment;

-   -   the gene is selected from the group consisting of:     -   a gene with a coding region having the nucleotide sequence set         forth in SEQ ID NO: 3; and     -   a gene derived from the gene with a coding region having the         nucleotide sequence set forth in SEQ ID NO: 3 with a         substitution and/or a deletion and/or an addition of one or more         nucleotides thereof, and being related to regulation of plant         root development.

In some embodiments of the use of the gene for regulating plant root development in the present disclosure,

-   -   the plant is rice.

In some embodiments of the use of the gene in the present disclosure,

-   -   a plant is treated with the peptide of different concentrations         to obtain a plant with shortened or lengthened root length;     -   in some embodiments of the use of the gene in the present         disclosure,     -   a recombinant expression vector 1 is introduced into a target         plant to obtain a transgenic plant with a shortened root length;     -   a DNA molecule set forth in SEQ ID NO:3 is inserted into a         multiple cloning site of a plasmid pCAMBIA 1300 to obtain a         recombinant-expression-vector-I-OsPEP1 overexpression vector.

In some embodiments of the use of the gene in the present disclosure,

-   -   a recombinant expression vector II is introduced into a target         plant to obtain a transgenic plant with a shortened root length:     -   a DNA fragment of the gene set forth in SEQ ID NO: 3 is ligated         to a transition vector pBSSK-in in sense and antisense         orientations, and then inserted into a plasmid pCAMBIA1300 to         obtain a recombinant-expression-vector-II-OsPEP1 RNAi expression         vector.

The technical scheme of the present disclosure is as follows:

The peptide PEP1, the precursor protein, and the gene encoding the same provided by the present disclosure are from the japonica rice Xiushui 134 (Oryza sativa L. ssp. Japonica cv. Xiushui134), in which the peptide is a peptide selected from the group consisting of the following (a) and (b), and the precursor protein, or the gene encoding the same are selected from the group consisting of (a). (b), (c), (d), (e) and (f):

-   -   (a) a peptide having the amino acid sequence set forth in SEQ ID         NO: 1;     -   (b) a peptide derived from the peptide having the amino acid         sequence set forth in SEQ ID NO: 1 with a substitution and/or a         deletion and/or an addition of one or more amino acid residues         and being related to plant development;     -   (c) a precursor protein having the amino acid sequence set forth         in SEQ ID NO: 2;     -   (d) a precursor protein derived from the precursor protein         having the amino acid sequence set forth in SEQ ID NO: 2 with a         substitution and/or a deletion and/or an addition of one or more         amino acid residues and being related to plant development;     -   (e) a gene having the nucleotide sequence set forth in SEQ ID         NO:3;     -   (f) a gene derived from the gene having the nucleotide sequence         set forth in SEQ ID NO: 3 with a substitution and/or a deletion         and/or an addition of one or more nucleotides and being related         to plant development;

The plant development is referred to a plant root length trait.

To facilitate purification of PEP1 in (a), tags including but not limited to those set forth in Table 1 are attached to an amino terminus or carboxyl terminus of the peptide having the amino acid sequence set forth in SEQ ID NO: 1.

TABLE 1 Sequence of the tags Tag Residue Sequence Poly-Arg 5-6 RRRRR (SEQ ID NO: 4) (usually 5) Poly-His  2-10 HHHHHH (SEQ ID NO: 5) (usually 6) FLAG  8 DYKDDDDK (SEQ ID NO: 6) Strep-tag II  8 WSIIPQFEK (SEQ ID NO: 7) c-myc 10 EQKLISEEDL (SEQ ID NO: 8)

PEP1 in (a) is artificially synthesized, or the gene encoding PEP1 is synthesized first, and then biologically expressed. The gene encoding PEP1 in (a) is obtained by deleting the codons of one or more amino acid residues in the DNA sequence set forth in SEQ ID NO: 3, and/or making one or more base pairs missense. The sequence encoding the peptide is obtained by mutating, and/or ligating the tags set forth in Table 1 at its 5′ end and/or 3′ end.

A gene encoding the protein also belongs to the protection scope of the present disclosure.

The gene OsPEP1 encoding the precursor protein is selected from a DNA molecule of the following 1) or 2) or 3):

-   -   1) a DNA molecule having the coding sequence set forth in SEQ ID         NO:3, that is, coding region of the gene having the nucleotide         sequence set forth in SEQ ID NO:3;     -   2) a DNA molecule that hybridizes with a DNA sequence defined         in 1) and encodes a protein of the same function under stringent         conditions;     -   3) a DNA molecule that is more than 90% identical to the DNA         sequence defined in 1) or 2) and encodes a protein of the same         function.

A recombinant expression vector, an expression cassette, a transgenic cell line or a recombinant bacterium containing the gene or antisense gene thereof all fall within the protection scope of the present disclosure.

The recombinant expression vector containing the gene OsPEP1 is constructed with an existing plant expression vector.

The plant expression vector includes, but is not limited to, for example, a binary Agrobacterium vector and a vector that is used for plant microprojectile bombardment, and the like. The plant expression vector may also contain the 3′ untranslated region of an exogenous gene, ie, a polyadenylation signal and any other DNA fragments involved in mRNA processing or gene expression. The polyadenylation signal guides the addition of polyadenylic acid to the 3′ terminus of the mRNA precursor, including but not limited to, for example, 3′ terminus of a Agrobacterium crown gall-inducing (Ti) plasmid gene (such as nopaline synthase Nos gene), a plant gene (such as a soybean storage protein gene) 3′-terminal transcribed untranslated regions, which has similar functions.

When OsPEP1 is used to construct a plant recombinant expression vector, any strong promoter or constitutive promoter can be added before the transcription initiation nucleotides, including but not limited to, for example, a cauliflower mosaic virus (CAMV) 35S promoter, and a Maize ubiquitin promoter, which can be used alone or in combination with other plant promoters; in addition, when the gene of the present disclosure is used for construction of a plant expression vector, an enhancer can also be used, including a translation enhancer or a transcription enhancer. These enhancer regions may be located near ATG start codons or adjacent region start codons, etc., but must share the same reading frame with the coding sequence to ensure the correct translation of the entire sequence. The translation control signals and start codons may be derived from a wide variety of sources, either natural or synthetic. Translation initiation regions can be from transcription initiation regions or structural genes.

In order to facilitate the identification and screening of transgenic plant cells or plants, the plant expression vector used may be processed, such as adding, including but not limited to, genes that are expressed in plants and encode enzymes or luminance compounds that produce color changes (GUS gene, luciferase gene, etc.), antibiotic-resistant markers (gentamicin marker, kanamycin marker, etc.) or chemical-resistant marker genes (e.g., herbicide-resistant genes), etc. In consideration of the security of transgenic plants, the transformed plants can be directly screened under stress without adding any selectable marker gene.

The recombinant expression vector may be the following (I) or (II):

-   -   (I) a recombinant expression vector containing the gene obtained         by inserting the DNA molecule as set forth in SEQ ID NO:3 into a         multiple cloning site of a plasmid pCAMBIA1300;     -   (II) a recombinant expression vector obtained by ligating a DNA         fragment as set forth in SEQ ID NO: 3 to a transition vector         pBSSK-in and conducting insertion into a plasmid pCAMBIA 1300         through forward and reverse ligation;

The plasmids pCAMBIA1300 and pBSSK-in in (I) or (II) are both obtained by engineering (already published).

The present disclosure also claims a method for cultivating a transgenic plant, including introducing the gene or gene fragment into a target plant by forward and reverse ligation to the transition vector pBSSK-in, in which the transgenic plant is a transgenic plant with altered root length as compared to that of the target plant.

Using any vector that can induce the expression of exogenous genes in plants, the OsPEP1 gene or gene fragment provided by the present disclosure is ligated to the transition vector pBSSK-in in sense and antisense orientations and then introduced into plant cells, so that a transgenic cell line and a transgenic plant with altered root length are obtained. Expression vectors carrying the whole or partial OsPEP1 gene that is forwardly and reversely ligated can be used to transform plant cells or tissue by conventional biological methods such as Ti plasmid, Ri plasmid, plant virus vector, direct DNA transformation, microinjection, electrical conductivity, and Agrobacterium-mediated method, and the transformed plant tissue is grown into a plant. The transformed plant host may be a poaceae plant, such as rice (e.g., Xiushui 134).

When a transgenic plant whose root length is longer or shorter than that of the target plant is to be cultivated, the method is to introduce (I) the recombinant expression vector into the target plant and a transgenic plant with shortened roots is obtained. When a transgenic plant whose root length is shorter than that of the target plant is to be cultivated, the method is to introduce the recombinant expression vector (II) into the target plant and a transgenic plant with shortened roots is obtained.

The present disclosure discovers a new rice root secreted peptide PEP1 and gene OsPEP1 encoding PEP1, and obtains a recombinant expression vector containing the gene or a partial fragment of the gene that is ligated to the transition vector pBSSK-in in sense and antisense orientations. The target plant is transformed with the recombinant vector, so that a transgenic plant with altered root length is obtained. Therefore. OsPEP1 can be used as a potential molecular breeding tool to improve plant yield by improving root length of plants.

In conclusion, the present disclosure isolates and identifies a peptide PEP1 that regulates rice root growth and development, and determines the gene OsPEP1 (LOC_Os11g09560) encoding PEP1 and precursor protein OsPEP1. That is, the present disclosure isolates and identifies a peptide PEP1 associated with plant root growth and development and gene OsPEP1 encoding PEP1. Exogenous application of PEP1 inhibits root growth and development. And a recombinant expression vector containing the gene encoding the peptide or part of the DNA of the gene is obtained, and a plant transformed with the recombinant expression vector can obtain a transgenic plant with altered root growth and development. Therefore, the peptide may be used as a plant growth regulator, and the gene encoding the same and its precursor protein may be used as a potential molecular breeding target for crop improvement, such as improving crop yield by regulating crop root growth and development.

BRIEF DESCRIPTION OF THE DRAWINGS

The specific embodiments of the present disclosure will be further described in detail below with reference to the accompanying drawings.

FIG. 1 shows that the gene OsPEP1 (LOC_Os11g09560) in Example 1 encodes a protein containing five amino acids (SDFDR, SEQ ID NO: 1);

-   -   A is the amino acid sequence of the protein encoded by the gene         OsPEP1 (MGEKERRLRVEGWMGRTEMIDRRRQRLHSGERERRLCVRKRMGSSDFDRGA         RFGGVDDGRLGEGTKRCEEMVGAIWDVGFERDNPDRSTRNEDVNISW, SEQ ID NO: 2),         the peptide PEP1 with 5 amino acid residues is underlined;     -   B illustrates LC-MS analysis of the peptide secreted by the         roots of wild-type rice plants;     -   C illustrates LC-MS/MS identification of Ser-Asp-Phe-Asp-Arg         (PEP1) (SEQ ID NO: 1), a wild-type rice plant root secreted         peptide, with a retention time of 12.25 minutes;     -   D illustrates LC-MS analysis of root secreted peptide of a         transgenic rice plant overexpressing LOC_Os11g09560;     -   E illustrates LC-MS/MS identification of the root secreted         peptide Ser-Asp-Phe-Asp-Arg (PEP1) (SEQ ID NO: 1) of a         transgenic rice plant overexpressing LOC_Os11g09560, with a         retention time of 12.26 minutes.

FIG. 2 illustrates the functional analysis of root secreted peptide PEP1 in Example 1;

-   -   A shows the phenotype of wild-type plants treated with different         concentrations of PEP1 for 7 days, with a scale bar of 5 cm;     -   B shows statistics of the primary root length of wild-type         plants treated with different concentrations of PEP1 for 7 days,         Data are shown as Mean±SD (n≥15 independent seedlings, three         biological replicates). Different letters indicate significant         differences (P<0.01, ANOVA, LSD test);     -   C shows the longitudinal section phenotype of root apical         elongation zone (upper left) and meristem (lower left) of         wild-type plants without PEP1 (−PEP1) treatment or that of the         elongation zone (top right) and meristem (bottom right) treated         with 10⁻⁶ M PEP1 (+PEP1) for 2 days. Bar=100 μm;     -   D is the statistics of the length of the meristem in panel C,         and data are shown as Mean±SD (n≥15 independent seedlings). ***         Significant difference from WT (P<0.001, Student's t-test);     -   E is the statistics of cell length in the elongation zone in C,         and and data are shown as Mean±SD (n≥15 independent seedlings).         *** Significant difference from WT (P<0.001, Student's t-test);

FIG. 3 is the expression profile of gene OsPEP1 in Example 2;

-   -   A shows expression level of the gene OsPEP1 detected by qRT-PCR         in rice roots, stems, leaves, and young ears, which were sampled         from 7-day-old rice seedlings:     -   B shows GUS staining of the Pro_(OsPEP1)::GUS transgenic plant         at the age of 7 days. Bar=1 cm;     -   C shows GUS staining of the primary root of the 2-day-old         Pro_(OsPEP1)::GUS transgenic plant. Bar=0.1 cm;     -   D shows the cross-section GUS staining of the primary root         elongation zone in C, with a scale bar of 100 μm;     -   E is the longitudinal section GUS staining of the primary root         meristem in C, with a scale bar of 100 μm.

FIG. 4 is the phenotypic analysis of transgenic plants overexpressing OsPEP1 in Example 2;

-   -   A shows the phenotype of 7-day-old seedlings of WT and plant         lines OE1, OE2 and OE3 overexpressing OsPEP1. Bar=5 cm;     -   B is the statistics of the primary root length of the         corresponding plants indicated in A. Data are means±SD (n≥15         independent seedlings). *** Significant difference from WT         (P<0.001, Student's t-test);     -   C shows expression level of the gene OsPEP1 detected by qRT-PCR         in the corresponding plants indicated in A. Data are means±SD         (n=3 biological replicates);     -   D shows longitudinal phenotype of the root tip elongation zone         (top) and meristem (bottom) of the wild-type WT and that of the         transgenic plant OE2 overexpressing OsPEP1 treated with 10⁻⁶ M         PEP1 for 2 days. Bar=100 μm;     -   E is the statistics of the apical meristem length indicated         in D. Data are means±SD (n≥15 independent seedlings, three         biological replicates). Different letters indicate significant         differences (P<0.01, ANOVA, LSD test);     -   F is the statistics of the cell length in the elongation zone         indicated in D. Data are means±SD (n≥15 independent seedlings,         three biological replicates). Different letters indicate         significant differences (P<0.01, ANOVA, LSD test).

FIG. 5 is the phenotypic analysis of transgenic plants underexpressing OsPEP1 in Example 2;

-   -   A shows the phenotype of 7-day-old seedlings of WT and that of         plant lines Ri1, Ri2 and Ri3 interfering OsPEP1. Bar=5 cm;     -   B is the statistics of the primary root length of the         corresponding plants indicated in A. Data are means±SD (n≥15         independent seedlings). *** Significant difference from WT         (P<0.001, Student's t-test);     -   C shows the expression level of the gene OsPEP1 detected by         qRT-PCR in the corresponding plants indicated in A. Data are         means±SD (n=3 biological replicates);     -   D is the longitudinal phenotype of the root tip elongation zone         (top) and meristem (bottom) of the wild-type WT and the         transgenic plant Ri2 overexpressing OsPEP1 treated with 10⁻⁶ M         PEP1 for 2 days. Bar=100 μm;     -   E is the statistics of the apical meristem length indicated         in D. Data are means±SD (n≥15 independent seedlings, three         biological replicates). Different letters indicate significant         differences (P<0.01, ANOVA, LSD test);     -   F is the statistics of cell length in the elongation zone         indicated in D. Data are means±SD (n≥15 independent seedlings,         three biological replicates). Different letters indicate         significant differences (P<0.01, ANOVA, LSD test).

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present disclosure is further described below in conjunction with specific examples, but the protection scope of the present disclosure is not limited to this.

The composition of the hydroponic medium is shown in Table 2.

TABLE 2 Composition of hydroponic culture medium Final Name Components MW Mol g/L 10000× (mM) Stock-1 MgSO4•7H₂O 246.3 0.547 134.800 10 ml 0.5470 (NH₄)₂SO₄ 132.0 0.365 48.200 0.3650 Stock-2 KH₂PO₄ 136.1 0.182 24.800 10 ml 0.1820 Stock-3 KNO₃ 101.1 0.183 18.500 10 ml 0.1830 Ca(NO₃)₂•4H₂O 236.0 0.366 86.400 0.3660 Stock-4 MnCl₂•4H₂O 197.9 0.005 0.990  1 ml 0.0005 H₃BO₃ 61.8 0.03 1.860 0.0030 (NH₄)₆Mo₇O₂₄•4H₂O 1235.9 0.001 1.236 0.0001 ZnSO₄•7H₂O 287.5 0.004 1.150 0.0004 CuSO₄•5H₂O 249.5 0.002 0.518 0.0002 Stock-5 NaFe-EDTA•3H₂O 421.1 0.100 42.100  4 ml 0.0400 MES MES 195.2 0.500 97.620 40 ml 2.0000

The detection results of gene expression levels in the following examples, unless otherwise specified, are all based on the target gene expression level of the wild-type plant Xiushui 134 as 1, and the target gene expression levels of other plants are compared with those of the wild-type plant.

Example 1. Acquisition of Rice Peptide PEP1 and Functional Study Thereof

1. Acquisition of Rice Peptide PEP1 and Gene Encoding the Same

(1). Acquisition of the Root-Secreted Peptide in Rice.

30 plump wild-type rice (Xiushui 134) seeds were treated with 0.5% nitric acid for 16-22 hours to break up the dormancy, and washed with tap water for 2-3 times, and then tap water was added to soak the seeds for germination acceleration in an incubator at 37° C. for two days until sprouting. During this period, the water was changed every morning and evening. Finally, the germinated seeds were sown on the nylon mesh floating on the nutrient solution (hydroponics medium), and cultured in an artificial climate chamber. The culture conditions in the artificial climate chamber were as follows: light for 14 hours, the average day and night temperature was 30° C./22° C., the light intensity was maintained at 200 μmol/m² s¹, and the humidity was 60%. After 10 days of culture, the medium was collected for subsequent concentration, extraction and precipitation of root exudates. The specific method is as follows: first, a rotary evaporator was used to concentrate the culture solution (500 ml) obtained in the previous step by 20 fold. Then, 20 ml of chlorophenol containing 1% NEM (N-ethylmorpholine, N-ethylmorpholine) was added and a resulting mixture was shaken for 1 minute at room temperature, centrifuged at 10,000 g for 10 minutes. A resulting organic phase was collected, and 20 times the volume of acetone was added to precipitate overnight at room temperature. Then a resulting mixture was centrifuged at 10000 g for 10 minutes, then a resulting precipitate was collected, washed with acetone for 3-4 times, and then vacuum dried to powder. Finally, the powder was sent to the company (Applied Protein Technology, co., Ltd) to identify 234 rice root-secreted peptides using liquid chromatography tandem mass spectrometry (LP-MS/MS).

(2). Acquisition of Candidate Genes Encoding Rice Root-Secreted Peptides.

Previous study have shown that the products of genes encoding some small signaling peptides (PSK, PSY1, CLV3/CLE) in Arabidopsis were cysteine-poor proteins with a length of 70-110 amino acids. Therefore, it is speculated in the present disclosure that if proteins encoded by certain genes in rice have these characteristics, the genes may be candidate genes encoding similar peptides. Based on this speculation, a total of 66,343 protein-coding genes from the Rice Genome Annotation Project (http://rice.plantbiology.msu.edu/index.shtml, March 2017) were downloaded, and then 12,678 protein-coding genes with a length of 50-150 amino acids were retrieved with MICROSOFT WORD 2003 and EXCEL 2003. The secreted peptide had a signal peptide sequence at its N-terminus. In the present disclosure, SignalP 4.1 server in the HMM webpage was used for screening and 704 protein-coding genes with a signal peptide at the N-terminus (P≥0.75) were obtained. Finally, EXCEL 2003 was used to exclude protein-encoding genes containing 6 or more cysteines and 416 candidate rice peptide-encoding genes were obtained.

(3). Identification of Rice Root-Secreted Peptide PEP1 and Gene Encoding the Same.

By comparing the 234 root-secreted peptides obtained by method (1) with the 416 putative rice peptide-encoding genes obtained by method (2), a novel peptide (Ser-Asp-Phe-Asp-Arg, SEQ ID NO:1) was identified in the present disclosure and candidate gene encoding the same (LOC_Os11g09560) (A in FIG. 1 ) was determined. In order to further confirm that LOC_Os11g09560 indeed encodes peptide PEP1, LC-MS/MS was used in the present disclosure to detect the root secretions of the LOC_Os11g09560 overexpressing transgenic plants. The results showed that the peak of this peptide in the root secretions of the LOC_Os011g09560 overexpressing transgenic plants were significantly enhanced (B-E in FIG. 1 ), indicating that the gene LOC_Os11g09560 indeed encodes peptide PEP1. Thereafter, the peptide (Ser-Asp-Phe-Asp-Arg, SEQ ID NO: 1) was named PEP1, and the gene encoding the LOC_Os11g09560 was named OsPEP1.

2. Functional Study of the PEP1

In the present disclosure, different concentrations of artificially synthetic PEP1 were used to treat rice seedlings (the concentrations were as described in A in FIG. 2 , and the treatment started after sowing and lasted for 7 days), and the results showed that exogenous application of PEP1 significantly inhibited rice primary root elongation (A and B in FIG. 2 ). In order to clarify the cellular basis of the PEP1 inhibitory effect on rice root elongation, we observed the section structure of these rice root tips, and found that after PEP1 treatment, the length of the meristem and cells in the elongation zone of rice root tips were significantly shortened. However, there were no significant changes in the quiescent center (as shown in the meristem of the root section, C-E in FIG. 2 ).

Example 2. Study on Expression Profile of the Rice Peptide PEP1 Encoding Gene OsPEP1

1. Expression of OsPEP1 in Different Rice Tissues Determined by qRT-PCR

Xiushui 134 rice was used as material, and cultured in normal nutrient solution (hydroponic culture medium) for 7 days. The roots, stems, leaves and leaf sheath were collected, and when the Xiushui 134 was in heading age, the young panicles were collected. All samples were frozen in liquid nitrogen and ground rapidly. Then the total RNA was extracted and reverse transcribed to obtain the cDNA. The expression of OsPEP1 in various tissues was detected by qRT-PCR. The results showed that the gene OsPEP1 was expressed in the different tissues tested in the present disclosure, and the expression level was higher in roots (A in FIG. 3 ). The detection primer sequences were as follows:

(SEQ ID NO: 9) 5′-GGCGTGGATGACGGGAGACT-3′; (SEQ ID NO: 10) 5′-TACATCCTCATTCCTCGTTG-3′,

The reaction system and procedures were as follows

-   -   2× Master: 2.5 μl     -   cDNA template: 0.1 μl     -   Primer-F (10 μM): 0.1 μl     -   Primer-R (10 μM): 0.1 μl     -   H₂O: 2.2 μl     -   Total: 5 μl;

The PCR procedures were as follows:

-   -   initiation: 95° C. for 1 minute;     -   amplification: 45 cycles of 95° C. for 10 seconds,     -   58° C. for 10 seconds, and     -   72° C. for 20 seconds;

Dissolution curve: 95° C. for 5 seconds,

-   -   65° C. for 1 minute,     -   97° C. cooling until 65° C.;     -   Cooling: 40° C. for 30 seconds;

2. The Expression of OsPEP1 in Different Rice Tissues determined by GUS Staining.

The DNA of Xiushui 134 rice was extracted, and used as a template for PCR amplification to amplify the 2 kb nucleotide sequence of the OsPEP1 promoter. The primers for PCR amplification were as follows:

(SEQ ID NO: 11) 5′-GCATGCCTGCAGGTCGACGTTTCTCAGCTACGCCCCTG-3′; (SEQ ID NO: 12) 5′-CCATGGTACCGTGGATCCCCGGAGCGCAGCCGTCGTCT-3′,

The obtained PCR product was inserted between the SalI and BamHI restriction sites of the vector pBI101.3-GUSplus modified in our laboratory by recombinant cloning (Lv et al., 2014) to obtain the Pro_(OsPEP1)::GUS vector. The vector was verified to be correct by sequencing. The constructed overexpression vector was transferred into Agrobacterium EHA 105 to transform Xiushui 134 plants, with reference to conventional steps, which were as follows:

-   -   (1) 500 μl of the cultured bacterial solution was added into a         1.5 ml centrifuge tube, centrifuged at room temperature, 4000         rmp for 2 minutes, and a resulting supernatant was removed. A         suspension with 30 ml of AAM-infected bacterial solution         containing 200 μmol/L acetosyringone was prepared, and the final         concentration of bacterial solution indicated by OD₆₀₀ is 0.01;         80 to 120 rice calli grown to a certain size (about 1 cubic         centimeter) were collected, put in Agrobacterium suspension, and         shaken for 5 minutes on a horizontal shaker;     -   (2) the calli were taken out and placed on sterile filter paper         to drain for 30 to 40 minutes;     -   (3) the calli were placed on a co-culture medium with a sterile         filter paper, and cultured in the dark at 25° C. for 3 days;     -   (4) the calli were taken out, and then washed with sterile water         for 5 to 6 times with constant shaking. The calli were washed         twice with sterile water containing 300 mg/L carbenicillin         sodium (Carb) and shaken on a horizontal shaker for 30 minutes         each time. Finally, the calli were placed on sterile filter         paper and drain for 2 hours;     -   (5) the air-dried calli were transferred to the selection medium         containing 300 mg/L carbenicillin sodium with the corresponding         selection pressure for a first round of selection, and cultured         at 28° C. for 14 days in the light;     -   (6) the initial calli of the positive calli were transferred to         the medium containing 300 mg/L carbenicillin sodium with the         corresponding selection pressure for a second round of         selection, and cultivated at 28° C. in the light until the         granular calli with resistance emerged (about 14 days);     -   (7) 3 to 5 positive calli with bright yellow color were taken         from different calli and then transferred into plastic jars with         differentiation medium, sealed with parafilm, and put in a         culture room (photoperiod: 16 hours of light) at constant         temperature (25° C.) for differentiation into seedlings (about         40 days); and     -   (8) when the seedlings grew to about 3 cm, the old roots and         calli were cut off from the base of the seedlings with scissors,         and put into the rooting medium to strengthen the seedlings         (about 1 week). The seedlings with well-differentiated roots,         stems and leaves were taken from the test tube (if the seedlings         grew to the top of the test tube, open the lid in time), the         sealing film was removed, an appropriate amount of distilled         water or sterile water (to prevent the growth of bacteria in the         medium) was added, and the seedlings were trained for 2 to 3         days. The agar was washed off and transplanted to grow in         hydroponic conditions in the greenhouse. Primers for the         gibberellin-resistant gene were used to detect transgenic plant,         and sequences of the primer were as follows:

(SEQ ID NO: 13) 5′-ATGAAAAAGCCTGAACTCACC-3′; (SEQ ID NO: 14) 5′-CTATTCCTTTGCCCTCGGACG-3′,

In the obtained transgenic rice of T2 generation, representative lines (transgenic plants with positive GUS staining) were selected for GUS staining to study the expression of OsPEP1 in different tissues of rice. It was showed that the gene OsPEP1 was mainly expressed in rice roots, especially the root cap zone of the root tip, and the cortex of the meristem and mature zones (B-E in FIG. 3 ).

Example 3. Functional Study of the Gene OsPEP1 Encoding the Rice Peptide PEP1

1. Construction of the OsPEP1 Overexpressing Recombinant Vector

The mRNA of Xiushui 134 was extracted and reverse transcribed into cDNA, and the cDNA was used as a template for PCR amplification to prepare the OsPEP1 sequence (DNA set forth in SEQ ID NO: 3). Primers for PCR amplification were as follows:

(SEQ ID NO: 15) 5′-ACGGGGGACGAGCTCATGGGAGAGAAGGAGCGGAG-3′; (SEQ ID NO: 16) 5′-GACTCTAGAGGATCCCAACTGATGTTTACATCCTCA-3′,

The obtained PCR product was inserted between the SacI and PstI restriction sites of the vector pCAMBIA1300 modified in our laboratory (Lv et al., 2014) by recombinant cloning to obtain the OsPEP1 overexpressing vector, and then the vector was verified to be correct by sequencing.

2. Acquisition of the OsPEP1 Overexpressing Transgenic Rice Plants

The OsPEP1 overexpressing vector constructed in step 1 was transferred into Agrobacterium EHA105 for transformation of rice Xiushui 134, and 32 positive transgenic plants were obtained. The specific steps were identical to step 2 of Example 2.

In the obtained T2 OsPEP1 overexpressing transgenic rice plants, three representative plants (OE1, OE2, OE3) were chosen for phenotypic analysis. It was showed that the primary root length of these transgenic plants were significantly shortened compared with that of Xiushui 134 (A and B in FIG. 4 ). The relative expression levels of endogenous OsPEP1 in Xiushui 134 and OsPEP1 overexpressing transgenic plants (OE1, OE2, OE3) were analyzed by quantitative real-time PCR (primers: GGCGTGGATGACGGGAGACT (SEQ ID NO: 9); TACATCCTCATTCCTCGTTG (SEQ ID NO: 10)). The results showed that the primary root length of those OsPEP1 overexpressing transgenic plants was positively correlated with the expression of OsPEP1 (see C in FIG. 4 ). In addition, the results of the observation of the section of these OsPEP1 overexpressing transgenic plants' root tips showed that the length of the meristematic region and the cell in the elongation region were significantly shortened, compared to that of Xiushui 134. Exogenous application of PEP1 could not restore the root tip defected phenotype of OsPEP1 overexpressing transgenic plants to the Xiushui 134 level (D-F in FIG. 4 ).

3. Construction of Recombinant OsPEP1 RNAi Vector

The mRNA of rice Xiushui 134 was extracted and reverse transcribed into cDNA, and the long cDNA was used as a template for PCR amplification to prepare a partial DNA sequence of OsPEP1:

(SEQ ID NO: 17) ACTCGGGAGAGAGGGAGCGCAGATTGTGCGTGAGGAAACGGATGGGAAGCA GCGATTTCGATCGAGGGGCGCGATTTGGGGGCGTGGATGACGGGAGACTGG GAGAGGGGACGAAGCGGTGTGAGGAGATGGTGGGAGCGATTTGGG.

Primers for PCR amplification were as follows:

(SEQ ID NO: 18) 5′-ACTCGGGAGAGAGGGAGCGC-3′; (SEQ ID NO: 19) 5′-CCCAAATCGCTCCCACCATC-3′,

The cloned PCR product was ligated with T vector (purchased from TAKARA), and the ligated plasmid was digested with PstI, BamH I and Pst I, Sal I respectively to obtain two fragments; the two fragments were ligated into the pBSSK-in vector (Wang et al. 2019) in two steps, pBSSK-in was first digested with Pst I and BamH I, and then ligated with one fragment, then digested with Nsi I and Sal I, and ligated with another fragment. Finally, the two fragments and intron were excised with Sac I and Sal I. and ligated into the same digested plant binary vector pCAMBIA1300 (Lv et al., 2014) to obtain an RNAi expression vector targeting OsPEP1. The RNAi expression vector targeting OsPEP1 was verified to be correct by sequencing.

4. Acquisition of OsPEP1 RNAi Transgenic Plants

The RNAi vector targeting OsPEP1 constructed in the above step 3 was transferred into Agrobacterium EHA105 for transformation of Xiushui 134, and 53 positive transgenic plants were obtained. The specific steps were identical to the step 2 in Example 2.

In the obtained T2 OsPEP1 RNAi transgenic plants, three representative plants (Ri1, Ri2, Ri3) were selected for phenotypic analysis. It was showed that the root length of these transgenic plants was significantly shortened compared to the wild type Xiushui 134 (see A and B in FIG. 5 ). The relative expression levels of endogenous OsPEP1 in Xiushui 134 and those OsPEP1 RNAi transgenic plants (Ri1, Ri2, Ri3) were analyzed by quantitative real-time PCR (primers: GGCGTGGATGACGGGAGACT (SEQ ID NO:9); TACATCCTCATTCCTCGTTG (SEQ ID NO: 10)). The results showed that the length of the primary root of those transgenic plants was positively correlated with the expression of OsPEP1 (C in FIG. 5 ); and results of section showed that the length of the meristem and the cells in the elongation zone of the those transgenic plants were significantly shortened compared to that of Xiushui 134. Additionally, exogenous application of PEP1 could restore the root tip defected phenotype of OsPEP1 RNAi transgenic plants to the Xiushui 134 level (D-F in FIG. 5 ).

Collectively, through comparative study of 234 rice root secreted peptides identified by LC-MS/MS and 416 candidate genes encoding rice peptides, in combination with the genetic analysis, a root-secreted peptide PEP1 (Ser-Asp-Phe-Asp-Arg, SEQ ID NO: 1) associated with rice primary root development was identified and its encoding gene OsPEP1 (LOC_Os11g09560) was determined. The results of physiological experiments of the present disclosure showed that exogenous application of PEP1 inhibited rice root elongation, and the genetic analysis of the present disclosure showed that overexpression or inhibition of OsPEP1 expression inhibited rice root elongation. These results suggest that the rice root secreted peptide may play an important role in rice root development as a signaling molecule, and may control the growth and development of rice roots by regulating the expression of OsPEP1.

Finally, it should also be noted that the above enumeration is only a few specific embodiments of the present disclosure. Obviously, the present disclosure is not limited to the above embodiments, and many modifications can be made. All modifications by those skilled in the art that can be directly derived or associated from the present disclosure shall be considered to fall within the protection scope of the present disclosure. 

1. A method for shortening or lengthening root length of a plant, comprising administering to the plant a peptide for regulating plant root development, wherein the peptide for regulating plant root development is selected from the group consisting of: a peptide having the amino acid sequence set forth in SEQ ID NO: 1; and a peptide derived from the peptide having the amino acid sequence set forth in SEQ ID NO: 1 with a substitution and/or a deletion and/or an addition of one or more amino acid residues and being related to the plant root development.
 2. The method of claim 1, wherein a precursor protein of the peptide is selected from the group consisting of: a precursor protein having the amino acid sequence set forth in SEQ ID NO: 2; and a precursor protein derived from the precursor protein set forth in SEQ ID NO: 2 with a substitution and/or a deletion and/or an addition of one or more amino acid residues and being related to plant development;
 3. A method for constructing a transgenic plant, wherein root length of the transgenic plant becomes shortened or lengthened; a gene encoding the peptide for regulating plant root development is selected from the group consisting of: a gene with a coding region having the nucleotide sequence set forth in SEQ ID NO: 3; and a gene derived from the gene with a coding region having the nucleotide sequence set forth in SEQ ID NO: 3 with a substitutions and/or a deletions and/or an addition of one or more nucleotides and being related to plant development.
 4. The method of claim 3, wherein the plant is rice.
 5. The method of claim 4, wherein the plant is treated with different concentrations of a peptide to obtain a plant with reduced or increased length; the peptide is selected from the group consisting of: a peptide having the amino acid sequence set forth in SEO ID NO: 1; and a peptide derived from the peptide having the amino acid sequence set forth in SEO ID NO: 1 with a substitution and/or a deletion and/or an addition of one or more amino acid residues and being related to the plant root development.
 6. The method of claim 3, comprising inserting a DNA molecule having the nucleotide sequence set forth in SEQ ID NO: 3 into a multiple cloning site of plasmid pCAMBIA1300 to obtain a recombinant expression vector I-OsPEP1 overexpression vector; and introducing the recombinant expression vector I-OsPEP1 overexpression vector into a target plant to obtain a transgenic plant with a shortened length.
 7. The method of claim 3, comprising inserting a DNA fragment of a gene having the nucleotide sequence set forth in SEQ ID NO: 3 is ligated to a transition vector pBSSK-in in sense and antisense orientations, and then conducting insertion into a plasmid pCAMBIA1300 to obtain a recombinant expression vector II-OsPEP1 RNAi vector; and introducing the recombinant expression vector II-OsPEP1 RNAi vector into a target plant to obtain a transgenic plant with a shortened length.
 8. A recombinant expression vector comprising a gene for regulating plant root development or an antisense gene thereof; wherein the gene for regulating plant root development is selected from the group consisting of: a gene with a coding region having the nucleotide sequence set forth in SEQ ID NO: 3; and a gene derived from the gene with a coding region having the nucleotide sequence set forth in SEQ ID NO: 3 with a substitutions and/or a deletions and/or an addition of one or more nucleotides and being related to plant development.
 9. The recombinant expression vector of claim 8, wherein the recombinant expression vector is the following (I) or (II): (I) a recombinant expression vector comprising the gene obtained by inserting the DNA molecule set forth in SEQ ID NO: 3 into the multiple cloning site of plasmid pCAMBIA1300; (II) a recombinant expression vector obtained by ligating a DNA fragment of a gene set forth in SEQ ID NO: 3 to a transition vector pBSSK-in in sense and antisense orientations and then conducting insertion into the plasmid pCAMBIA1300.
 10. (canceled)
 11. (canceled)
 12. (canceled)
 13. The method of claim 6, wherein the plant is rice.
 14. The method of claim 6, wherein the plant is treated with different concentrations of a peptide to obtain a plant with reduced or increased length; the peptide is selected from the group consisting of: a peptide having the amino acid sequence set forth in SEQ ID NO: 1; and a peptide derived from the peptide having the amino acid sequence set forth in SEQ ID NO: 1 with a substitution and/or a deletion and/or an addition of one or more amino acid residues and being related to the plant root development.
 15. The method of claim 6, wherein the plant is rice.
 16. The method of claim 6, wherein the plant is treated with different concentrations of a peptide to obtain a plant with reduced or increased length; the peptide is selected from the group consisting of: a peptide having the amino acid sequence set forth in SEQ ID NO: 1; and a peptide derived from the peptide having the amino acid sequence set forth in SEQ ID NO: 1 with a substitution and/or a deletion and/or an addition of one or more amino acid residues and being related to the plant root development. 